An ultrasonic diagnostic apparatus transmits an ultrasonic wave to the inside of an object by an ultrasonic probe including plural ultrasonic transducers, receives a reflected echo signal corresponding to the structure of body tissue from the inside of the object, generates a tomographic image, for example, a B-mode image on the basis of the reflected echo signal, and displays the B-mode image for diagnosis.
In recent years, as disclosed in PTL 1, an elastic image showing the hardness or softness of tissue of a tomographic plane has been generated by measuring an ultrasonic reception signal (RF signal) while pressing an object with an ultrasonic probe using a manual or mechanical method. That is, displacement of each part of tissue occurring due to pressure is calculated on the basis of frame data of a pair of RF signals with different tissue pressure states, frame data of elastic information such as an elastic modulus or distortion is calculated on the basis of the frame data of the calculated displacement, and an elastic image is generated and displayed on the basis of the elastic frame data.
Incidentally, the displacement of tissue changes in accordance with pressure force. Accordingly, distortion of tissue of the same part increases if the pressure is large. For this reason, an elastic image generated on the basis of distortion is only to represent a relative display of distortion of each part on the elastic image, and it is not possible to evaluate the hardness quantitatively with the elastic image.
Regarding this point, as disclosed in PTL 2, displaying an elastic image of a certain tomographic plane of an object, setting two regions of interest (ROIs) on the displayed elastic image, and calculating and displaying the two-dimensional elastic ratio of the elastic information of the two set regions of interest are known. According to this, the two-dimensional elastic ratio of the elastic information of two regions of interest is calculated as an index value. Therefore, the operator can evaluate the hardness of tissue of a diagnostic part quantitatively regardless of pressure force.